Apparatus



April 18, 1967 A. w. GEssNx-:R ETAL APPARATUS Filed Nov. 15, 1965 INVENTORS Adolf W. Gessner Theodore J. Kayhar Gordon Dibble www ATTORNEYS United States Patent Ofice 3,314,399 Patented Apr. 18, 1967 3,314,399 APPARATUS Adolf W. Gessner, Montclair, and Theodore J. Kayhart,

Caldwell, NJ., and Gordon L. Dibble, New York,

NSY., assignors to The Lummus Company, New York,

N.Y., a corporation of Delaware Filed Nov. 15, 1965, Ser. No. 507,750 11 Claims. (Cl. 122-7) This invention relates generally to recovery furnaces and, more particularly to a pulping liquor recovery furnace for high sulfur reduction.

Advances in practices in the pulping art have caused a greater sulfur reduction load to be placed on the recovery furnaces. For example, in certain pulping processes, the percentage suliidity of the cooking liquor is found to be from 50% to 90%, greater than in a conventional kraft liquor (percentage suliidity being equal to 100 (Na2S)/ (NaZS-l-NaOH-l-NazCOa), all quantities being expressed in moles). In some pulping processes, the alkali-to-wood ratio employed within the digester is greater than the ratio used in the conventional cooking. This larger ratio causes a larger amount of sulfur Per unit of liquor burned to circulate through the recovery furnace. Also, it was discovered by prior Workers that by oxidizing the sulfide to thiosulfate while still in the black liquor prior to the introduction of black liquor into the direct contact evaporator, sulfur losses as HZS in the evaporator steam condensate and direct contact evaporator off-gas could be eliminated. However, in order to compensate for the heat liberated by this oxidation, a larger amount of heat must be supplied in the recovery furnace to reduce the sulfur than would need to be reduced in a conventional kraft process.

As a result of the greater alkali/ Wood ratio, the higher sultidity, the spent liquor oxidation, or the combination of these factors, a substantially greater sulfur reduction load is placed on the furnace when compared with the conventional liquor recovery furnace. A considerable increase in the heat per unit of liquor is required, because of the endothermic nature of the reduction reactions of sodium sulfate, thiosulfate and sulte to sullide. In the conventional recovery furnace, most of the heat released from the primary combustion of the charred liquor to CO, is radiated to the boiler tubes which surround the hearth zone and also to the luminous gases in the secondary combustion zone of the furnace. Therefore, this heat is not available to the reduction reactions taking place in the hearth of the furnace.

Accordingly, it is the object of this invention to provide an improved recovery furnace.

It is also an object of this invention to provide a recovery furnace wherein additional heat for sulfur reduction is available.

It is further the object of this invention to provide a recovery furnace wherein the net radiation heat ow between the hearth and secondary combustion zones is reduced.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a schematic diagram, in section, of a pulping liquor recovery furnace in which one embodiment of the present invention is included;

FIGURE 2 is a cross-section taken along lines 2--2 of FIGURE l; and

FIGURE 3 is a cross-section taken along lines 3 3 of FIGURE 1.

Briefly, the present invention comprises two modifications of a conventional recovery furnace. The first modification is that a refractory obstacle is placed above the hearth zone thereby reducing the net radiation flow and causing additional heat to be available for the sulfur reduction. The second modification is that the boiler tubing which normally su-rrounds the hearth zone in a kraft recovery furnace is removed.

Now referring to FIGURE 1, a refractory-lined recovery furnace is generally indicated at 1. The black liquor enters furnace 1 through inlet tubes 2 and 3 located part way up the sides of furnace 1. Primary air travels through inlet tubes 4 and 5 and is injected into a hearth zone, generally shown as 6. The inlet tubes 2 and 3 inject the black liquor into a secondary combustion zone, generally denoted as 7, also into which secondary air may be introduced through a tube attached to aperture 8. Boiler feed water travels through =a tube 9 into a steam drum 10, then through a plurality of tubes 11 into a mud drum 12. Steam is withdrawn through tube 13- attached to steam drum 10. Tubes 9, 11 and 13, steam drum 10 and mud drum 12 are located near the top of furnace 1. A refractory battle 14 has been provided near tubes 11 to assist in the heating of the water. The inherent heat of the black liquor causes decomposition of the lignin and vaporization of the water. The black liquor travels into hearth zone 6 in which the sulfur reduction reactions occur.

The resulting smelt accumulates `at the bottom of furnace 1 in a layer 15 and is withdrawn from layer 15 through an outlet tube 16.

The present invention changes the structure of the foregoing conventional recovery furnace 1 by irst omitting the boiler tubes which would normally surround hearth zone 6. The temperature difference between the boiler tubes and a hearth zone of the conventional furnaces causes heat to ow from said hotter hearth zone to said cooler boiler tubes. As a result of eliminating the boiler tubes, the heat normally lost thereto from hearth zone 6 is retained and is utilized in the endothermic reduction of the sultes, thiosulfates and sulfates to sulfide. The second modification is that below inlet tubes 2 and 3 and Aabove inlet tubes 4 and 5, radiation baflies 17, 18 and 19 have been inserted. Bales 17 and 18 extend downward from the sides of furnace 1. Baffie 19 has the shape of an inverted V, the apex of which is placed in the open space between baffles 17 and 13. Additional support for batiies 17 and 18 may be provided by a plurality of support means 20 and 21 positioned like a brace between said balies 17 and 18 and the walls of furnace 1. Baffles 17 and 18 extend horizontally to a point further toward the center of furnace 1 than are the ends of bafe 19, so :that in viewing furnace 1 from the top, the ends of baies 17 and 19 and the ends of baffles 18 and 19 appear t-o overlap.

Alternatively, baiiies 17, '18 and 19 could be replaced by lany obstacle which would effectively block the line of sight between hearth Zone 6 and secondary coubustion zone 7. Whether baffles or some other obstacle are used, they must be shaped so as not to trap the black liquor traveling between secondary combustion zone 7 and hearth zone 6, and so as not to obstruct inlet tubes 2 and 3. The batiies or obstacles may be made a par-t of the internal furnace construction to increase their ability to withstand operational stresses and strains.

Baifles 17, 18 and 19 are constructed out of a refractory material such that they can attain a temperature up to about 2300 F. The construction of the downward slanting baiiies 17 and 18 and the inverted V of bafe L19 causes most of the heat radiated upward from hearth zone 6 to be reected back into hearth zone 6, thereby preventing said radiated heat from seeking out the cooler, upper parts of furnace 1. The heat released in hearth zone 6 is thereby available for the endothermic reduction reactions, while the heat released in secondary combustion zone 7 performs the functions of evaporating water in the black liquor, charring the lignin in the black liquor, and vaporizing the water in tubes 1-1 and mud drum 112. As in a conventional unit, after lgiving up heat to tubes 11 the hot gases pass to a conduit 24 for transmission of the .gases to other recovery operations and eventual venting. s

The overlap of bafhes x17 and 18 over bafhe 19 is illustrated in FIGURE 2, and the construction of bathe 19 is illustrated in FIGURE 3. In particular, it should be noted that suppport frame 22. extends to the walls of the furnace and supports the refractory lining 23.

Structural steel members in this structure are water cooled to maintainrnechanical strength.

It will be understood that various changes in the details, steps, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as defined in the appended claims.

What is claimed is:

=1. A blackliquor recovery furnace comprising:

(a) a furnace housing containing a hearth combustion zone and a secondary combustion zone, said secondary combustion zone being above the hearth combustion zone;

(b) means for introducing black-liquor into said secondary combustion zone;

(c) means separating said zones, said means preventling line of sight between said Zones but permitting liquor to how from said secondary combustion zone to said hearth combustion zone; and

(d) means for introducing air into each of said Zones.

`2. The furnace of claim 1 further comprising a heat recovery means located in the upper portion of said secondary combustion zone.

3. The conventional recovery furnace claimed in claim -1 wherein the means for separating said zones is made of .a refractory material capable of withstanding a temperature of about 2300" F.

4. The conventional recovery furnace claimed in claim 1 wherein the means for separating said zones is shaped so as to rehect most or the heat back to the zone from which it came.

5. The vfurnace .as claimed in claim 1, wherein said means for separating said zones consists of bafhes.

6. The furnace as claimed in claim 1, wherein said means for separating said zones is an integral part of the furnace construction,

7. A recovery furnace as claimed in claim 11, wherein said lirst baihes extend sufliciently toward the center and said second bathe extends sufciently toward the walls to prevent any substantial line-of-sight communication between said upper and lower zones.

8. A recovery furnace as claimed in claim 2, wherein said recovery means comprises boiler tube means with huid supply and outlet means associated therewith, and additionally comprising bathe means protecting said tube means from radiant heat from said upper zone.

9. A recovery furnace as claimed in claim 41t), wherein said bathe means are formed integrally with said housing.

10. A black-liquor recovery furnace comprising:

(a) a housing, including a secondary combustion chamber and a hearth combustion chamber;

(c) means separating said chambers said means including, a first bathe means extending from the sides of said housing, and a second central bathe means, said hrst and second bathe means being positioned so that a portion thereof are in an overlapping relationship.

11. A black-liquor recovery furnace comprising:

4a furnace housing having an upper, secondary combustion zone and a lower, hearth combustion zone;

bathe means separating said upper and lower zones but allowing huid flow therebetween, said bathe means comprising rst baihes extending from the sides of said housing and a second, central bathe at a slightly different level, said first and second bathes presenting downwardly-sloping surfaces to downwardly-flowing huid;

black-liquor inlet means communicating with said upper zone; Y

outlet means communicating with said lower zone in the hearth region thereof;

air inlet means communicating with each said zone;

heat recovery means located only in the upper portion of said upper zone; and

outlet means positioned so as to remove combustion gases after passage through said recovery means.

References Cited by the Examiner UNITED STATES PATENTS 620,752 3/ 1899 Dorenfeldt 122--7 1,794,006 2/1931 Falla 112-7 2,591,188 4/ 1952 Nilsson.

FOREIGN PATENTS 548,873 10/1942 Great Britain.

KENNETH W. SPRAGUE, Primary Examiner, 

1. A BLACK-LIQUOR RECOVERY FURNACE COMPRISING: (A) A FURNACE HOUSING CONTAINING A HEARTH COMBUSTION ZONE AND A SECONDARY COMBUSTION ZONE, SAID SECONDARY COMBUSTION ZONE BEING ABOVE THE HEARTH COMBUSTION ZONE; (B) MEANS FOR INTRODUCING BLACK-LIQUOR INTO SAID SECONDARY COMBUSTION ZONE; (C) MEANS SEPARATING SAID ZONES, SAID MEANS PREVENTING LINE OF SIGHT BETWEEN SAID ZONES BUT PERMITTING LIQUOR TO FLOW FROM SAID SECONDARY COMBUSTION ZONE TO SAID HEARTH COMBUSTION ZONE; AND (D) MEANS FOR INTRODUCING AIR INTO EACH OF SAID ZONES. 